Carcinoid tumors are rare and cause either no or few nonspecific symptoms. Therefore, patients with carcinoid tumors most often present late in the course of their illness when there is already progression to an incurable state as a result of metastatic disease. At present there are neither practical population screening tests nor effective therapies and hence the 5 year survival rate is low. Due to the rareness of sporadic carcinoid tumors, large scale genetic analysis and development of sensitive and specific diagnostic tests have not been successful. While kindreds with familial carcinoid tumors that are not ascribable to known genetic syndromes are exceedingly rare, they provide a unique opportunity to facilitate the identification of the responsible gene mutation. In addition, the mutated gene in the rare familial form may also underlie the origin of the more common sporadic occurrence of carcinoid tumors. We propose to study families in which there are at least two known affected members with carcinoid tumors. We aim to diagnose patients with early and therefore potentially curable occult disease. Therefore, family members who have up to a 50% lifetime risk of harboring a carcinoid tumor will undergo an intensive diagnostic evaluation using biochemical, endoscopic and imaging modalities at initial and subsequent two year follow up encounters. Early phenotypic assignment of affected family members and collection of germline and tumoral DNA from multiple kindreds should also facilitate the genetic analysis leading to the identity of the disease gene. Evaluation of affected family members at varying stages of disease will contribute to our understanding of the natural history of carcinoid tumors and the relative utility of a variety of diagnostic and surveillance tests. Hopefully, such knowledge gained will also be applicable to patients with carcinoid tumors occurring sporadically or in the setting of other familial cancer syndromes. There is no planned treatment for patients with existing or newly diagnosed primary or metastatic carcinoid tumors. However, these patients may be evaluated by consultation with oncology and surgery for potential treatment on their service under their preexisting protocols.